For a number of years, keypad structures used for certain classes of telephone apparatus have been made of silicone elastomer, a material described in more detail, for example, in the publication, "Polymers for Electronic Packaging," C. P. Wong, 43rd Electronic Components and Technology Conference, Components, Hybrids and Manufacturing Technology Society, IEEE, 1993, incorporated herein by reference. Such a keypad, for example, may include a plurality of raised portions each displaying a different digit or other alphanumeric symbol. On the underside of each raised portion is a conductive element, such as a carbon-filled silicone portion, which is capable of completing a circuit when the raised portion is depressed by an operator. Such keypads offer advantages of low cost, ease of assembly and ease of use.
Statistical data on the use of telephone apparatus employing silicone elastomer keypads have shown a significantly high average failure rate. It is of course important that the long-term reliability and dependability of telephone apparatus be maintained as high as is possible.